Fifty percent of Americans use some form of alternative medicine. Herbal remedies and megavitamins are available at most malls and grocery stores, many hospitals offer acupuncture and energy healing, and shares in the companies that comprise the multibillion dollar alternative medicine industry are traded on the stock exchange. With such mainstream acceptance, why is alternative medicine still considered “alternative”?

In his new book, “Do You Believe in Magic? The Sense and Nonsense of Alternative Medicine,” Paul A. Offit asks this question and another: Why is some alternative medicine considered medicine at all?

Offit, chief of pediatric infectious diseases at Children’s Hospital of Philadelphia and professor of vaccinology and pediatrics at the University of Pennsylvania, makes no secret of his bias against therapies and theories that have not been subjected to randomized controlled trials — or of his scorn for the celebrities, “quack” doctors, and others who tout unproven benefits or harmfulness of certain treatments. He dedicates his book to “all the science writers, science advocates, and science bloggers who have dared proclaim that the emperors of pseudoscience have no clothes.”

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“Do You Believe in Magic?” is a briskly written, entertaining, and well-researched examination of those whom Offit considers “unclothed emperors”: purveyors of miracle cancer cures, fountains of youth, and the theory that vaccines cause autism.

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Offit begins his book with a the case of Joey Hofbauer, a 10-year-old boy who died in 1980 of Hodgkin’s disease. Joey’s parents eschewed radiation and chemotherapy, often curative for Hodgkin’s in children, and, instead, took him to Jamaica for treatments with laetrile. This drug, produced from apricot pits, gained popularity in the 1970s as a “more natural” cancer therapy. Thousands went to Mexico or the Caribbean seeking laetrile, which was illegal in many states, and repeatedly proven ineffective against cancer. By the time of Joey’s death, several states had legalized laetrile, influenced not by science but by lobbying groups, the testimony of actor and cancer patient Steve McQueen, and public opinion. “By the end of the 1970s,” Offit writes, laetrile wasn’t just a drug; it was a social movement.”

Offit points out that the key elements of the laetrile story can be seen today in Jenny McCar-thy’s crusade against vaccines, Dr. Oz’s promotion of coffee enemas and homeopathy, and celebrity anti-aging programs: patients eager for relief, distrust of conventional medicine, charismatic spokespeople — and huge profits. He highlights the irony that those who decry “Big Pharma” embrace alternative medicine, which is highly lucrative and virtually unregulated.

Even before writing “Do You Believe in Magic?,” Offit had ardent admirers and detractors. The coinventor of a vaccine against rotavirus, which causes the diarrheal disease that kills hundreds of thousands of children worldwide annually, Offit is a hero of modern medical science to many. His financial ties to the vaccine industry and his outspoken opposition to the antivaccine movement have made him a villain to many others.

Reportedly, Offit gets a lot of hate mail. “Do You Believe in Magic?” will no doubt add to the pile. Feelings about alternative medicine run so strongly that Offit’s new book is more likely to validate the opinions of readers who agree with him than convince those who don’t. But Offit’s clear, well-documented arguments may make even the most avid fans of glucosamine for aching joints, vitamin C to prevent colds or other forms of alternative medicine pause to ask why they are spending money and even risking their health on treatments that have been shown ineffective.

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Offit is not dismissive of the suffering of people who seek alternative healing, he just doesn’t feel suffering is a reason to abandon science. He writes that if a treatment isn’t proven to work, it should be abandoned. If a theory is disproven repeatedly, it should be discarded. Conversely, if natural remedies, such as those derived from foxglove (digitalis) or willow leaves (aspirin), are truly effective, they should be prescribed. “ ‘There’s a name for alternative medicines that work,’ ” Offit writes, quoting a colleague, “ ‘it’s called medicine.’ ”

Suzanne Koven is a primary care internist at Massachusetts General Hospital and writes the monthly “In Practice” column for the Globe. She can be reached at inpracticemd@gmail.com. Read her blog on Boston.com/Health.